Dry fibrous material for subsequent resin infusion

ABSTRACT

Disclosed herein is a dry, self-supporting fibrous material, the fibers of which have been treated with a binder composition. The fibrous material can be slit into tapes or tows that are suitable for use in an Automated Tape Laying (ATL) or Automated Fiber Placement (AFP) process. This fibrous material is suitable for forming preforms which are configured to receive a matrix resin by resin infusion in the manufacturing of structural composite parts.

BACKGROUND

The present disclosure is related to the field of preforming and resininfusion manufacturing of structural composite components.

In recent years, the aerospace and automotive industries showedincreasing levels of interest in the application of resin infusionprocesses to manufacture structural components.

Dry, flexible and pre-formable fibrous products can in fact havesignificant advantages over standard pre-pregged materials due theirlonger shelf life and applicability to more complex geometries andaround narrow radii.

The aspects of interdependence and criticality of the materialsselection and processing stages are of special significance in automatedlay-down/infusion processes wherein the stages of fiber placement,preforming and resin injection are distinct in phase, but coupled inmaterials selection and processing related aspects.

Sizings and binders can in fact simultaneously affect processing andthermo-mechanical performance of composite structures.

Composites cure kinetics and thermo-mechanical properties can be in factinfluenced by the formation of an interface region between the fibrouscomponent and the hosting matrix. In addition fiber/sizing/resininteractions occurring during the infusion stage can affect wet-out andlocal flow behavior through the development of stoichiometric andcompositional imbalanced regions.

Most fibers and fibrous products used in composites are coated withsizings, binders, and/or finishes that serve multiple purposes,including facilitating handling, protection of the fibers fromcompaction and process induced damage, aiding in compatibility andwetting of the fibers by the resin, and overall enhancement of thecomposites performance.

Several dry unidirectional tape products utilize a carbon web ofunidirectional carbon fibers that has been thermally or adhesivelybonded onto a carrier fabric or scrim to support the unidirectionalcarbon fibers. Several commercial versions are available from V2Composites, Sigmatex and other textile producers. The limitations ofthese current products lies in the inability to slit and apply theseproducts via an automated lay down process without deforming and frayingthe edges.

In other conventional materials such as the NCF textile (non-crimpfabric), the unidirectional (UD) fiber tows are held together bystitching threads crossing over several carbon tows. In some occasions,very fine fibers are laid across the cross-web direction to provide morelateral stability to the UD fiber tows. In this case, the tows are notspread out and inter-tow gaps as wide as 2 mm exist. Saertex andSigmatex supply this type of products.

Another conventional method of forming a dry unidirectional tape is thetechnique comprising spreading a web of fibers and holding the spreadfibers with a binderized fine threads usually made of epoxy coated glassthreads or polyester or polyamide threads with low heat activationpoint, running across the width of the tape and holding the spreadfibers together. The holding threads are not woven with the web fibersbut deposited on the top and/or bottom faces of the web. In this type ofproduct, web fibers are usually well spread out leaving very little towdefinition and inter-tow gaps, similarly to standard spread tapeproduced on prepreg tape machines.

It is believed that none of the state of the art binder compositions ormaterial solutions satisfies the physical, thermo-mechanical and processrequirements for the production of dry, fibrous materials that aresuitable for used in Automated Tape Laying (ATL) and Automated FiberPlacement (AFP) to form preforms for subsequent resin infusion incomposite part manufacturing.

SUMMARY

Disclosed herein is a dry, self-supporting fibrous material ofstructural fibers to be used for subsequent resin infusion. The fibrousmaterial contains structural fibers that are bound together by a bindercomponent present in an amount of 15% by weight or less of the material.The binder component does not form a continuous film at the surface ofthe fibrous material. The fibrous material is characterized in that itis fluid-permeable, more specifically, it is permeable to liquid resins,it frays less upon slitting, and has a lower dimensional variation thanthe same fibrous material without binder.

Also disclosed herein is a binder composition for applying onto thestructural fibers. The binder composition is a water-borne dispersioncontaining (i) one or more polymers selected from: polyurethane;polyhydroxyether; a copolymer thereof; a reaction product thereof; and acombination thereof; (ii) a cross-linker; and optionally, (iii) acatalyst of sufficient acid strength to catalyze the crosslinkingreaction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a unidirectional non-crimp fabric (UD NCF).

FIG. 2 illustrates a spread out carbon fiber web with binder yarns.

FIG. 3 is an SEM image showing veil side of a binder-treated, fibrousmaterial according to one example.

FIG. 4 is an SEM image showing fiber web side the fibrous material shownin FIG. 3.

FIG. 5 is a graph showing the relative volume of resin infused through apreform thickness as a function of time, according to an example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The technological challenges connected to the manufacture ofnarrow-width, fibrous products suitable for automated lay-up processes,more specifically, ATL and AFP, determined the need for bindercompositions capable of providing cohesion and integrity to the fibersduring the slitting, handling and lay-down processes and preventing thecreation of fuzzy edges which can dramatically affect the process speedand throughput.

One aspect of the present disclosure lies in a dry, self-supportingfibrous material of structural fibers that has been treated with aunique liquid binder composition, wherein the resulting binder-treatedfibrous material is permeable to liquid resin, and the bindercomposition does not form a continuous film at the surface of thefibrous material. The binder composition is present in an amount of 15%or less by weight, e.g. 0.1 and 15% by weight, based on the total weightof the fibrous material, and the structural fibers is the majorcomponent of the fibrous material (e.g. greater than 50% by weight basedon the total weight of the fibrous material). The starting fibrousmaterial to be treated with the binder composition may be in the form offibers (including unidirectional or multi-directional fibers), yarns,tows, woven or nonwoven fabrics.

In one embodiment, a dry, unidirectional fiber web composed ofunidirectional structural fibers (e.g. carbon fibers) in areal weightsin line with state of the art prepreg tape is bonded to a nonwoven veilof thermoplastic fibers, using a continuous process on a hot-melt typeproduction line. The bonded structure of unidirectional tape/veil isthen coated with the liquid binder composition disclosed herein. In oneembodiment, the nonwoven veil contains randomly-arranged thermoplasticfibers that are soluble in epoxy resins. The detailed description of theresin-soluble veil may be found, for example, in the published patentapplication US 2006/0252334. The unidirectional tape may be made by aconventional prepreg method of spreading a web of structural fibers andusing a tape machine to do so. A resin-soluble thermoplastic veil isthen laminated to the spread structural fibers to keep the tape form.

In another embodiment, a nonwoven veil composed of structural fibers(e.g. carbon fibers) is laminated to a fiber web (i.e., a web of spreadfibers), and a thermoplastic modified epoxy-based binder is coated ordeposited onto the veil, then the veil is laminated to the fiber webusing a prepreg tape machine to form the dry tape. Subsequently, the drytape is coated by dip-coating with the water-borne binder compositiondisclosed herein. The water-borne binder composition disclosed hereindoes not completely coat the modified epoxy-based binder. The resultingbinder-coated tape is slit into narrow tapes or tows of desired widthsthat are suitable for ATL/AFP, for example, 24 in or less, or 1.5 in orless. In one embodiment, the modified epoxy-based binder contains one ormore multifunctional epoxy resins and a thermoplastic polymer, and maybe in the form of particles or film. The incorporation of the modifiedepoxy based binder on the surfaces of the fiber web and veil can furtherfacilitate the bonding of the slit tape/tow to the tool surface or to apreviously laid down tape/tow.

The unique liquid binder composition disclosed herein is used to coat orinfiltrate the fibrous material. The binder-treated fibrous material issuitable for the fabrication of preforms, which are subsequently infusedwith liquid resin. As such, the binder-treated fibrous material is afluid-permeable product that is very low in resin content (i.e., thebinder resin content not the matrix resin to be injected later) prior toresin infusion. The resin-infused preforms are then cured to formcomposite parts.

The liquid binder composition as discussed above is based on awater-borne dispersion containing: (i) one or more polymers selectedfrom polyhydroxyethers, polyurethanes, copolymers thereof, reactionproducts thereof, or combinations thereof; (ii) a cross-linker; andoptionally, (iii) a catalyst.

In one embodiment, the binder composition is applied as a polymeremulsion to coat or infiltrate the fiber yarns/tows or fibrous textilesat room temperature. Water is then removed/evaporated according to acontrolled time/temperature profile to achieve the desired physicalproperties balance. The resulting coated yarns/tows or fibrous textilesare suitable for use with automatic tape and fiber laydown technologiessuch as automated tape laying (ATL) and automated fiber placement (AFP)to manufacture preforms, which are configured for receiving liquidmatrix resin in a subsequent resin infusion process. The bindercomposition may be applied to the yarns/tows or textile in aconcentration between the 0.1 and 15% by weight relative to the totalweight of the final product.

When the binder composition is applied to fibrous materials in largesizes, the resulting binder-treated materials can be slit into elongatedtapes or tows with narrow width so that they are suitable for use in theproduction of dry fiber preforms via ATL and AFP processes. The bindercomposition of the present invention consistently improves the handlingand slitting of the coated or infiltrated yarns/tows or fibrous textilesinto narrower products and their shaping into the preform before theyare infused with resin. The binder composition also providesimprovements in the bond strength between the coated fibrous componentand the composite matrix after the infusion and cure without undulysacrificing important laminates physical properties such as the glasstransition temperature (Tg) in dry and hot/wet (H/W) conditions and themechanical performance.

The performance in producing preforms and composite parts is increasedby using binders that help stabilize the unidirectional structural fibertextile for slitting into narrow tapes, help the tape laydown processand preform manufacture, and do not interfere with the resin infusionprocess nor the mechanical performance of the final composite part.Further, in some embodiments, a very light, nonwoven veil is bonded tothe unidirectional structural fiber textile prior to binder coating andslitting. The veil enhances the in-plane resin diffusion during theresin injection cycle. In some aspects, perforations of theuni-directional structural fiber textile may be helpful to improve theresin diffusion through the thickness of the textile material during theresin infusion process.

Resulting benefits of using a dry unidirectional tape in an ATL/AFPprocess include the efficient creation of a required preform throughreduced touch labor, high lay-down rates and the ability to create thepreform in an in-situ fashion, eliminating the need for any dedicatedpreforming cycle of heat and pressure. Compared to more traditionaltextile routes dry ATL/AFP is expected to return a much reduced level ofmaterial scrap due to the elimination of any need to nest large pliesfrom a textile roll.

The resulting benefits for composites made of a dry unidirectional tapeover traditional textiles include improved mechanical properties, verygood fiber volume fraction and excellent cured ply thickness (CPT) thatis not deteriorated by the addition of the very light veil. Thecomposite fiber volume fraction is calculated using the followingequation:

$V_{f} = \frac{W_{f}\rho_{m}}{{W_{m}\rho_{f}} + {W_{f}\rho_{m}}}$

-   where:-   V_(ƒ)=Fibers volume fraction-   W_(ƒ)=Weight of fibers-   W_(m)=Weight of matrix resin-   P_(ƒ)=Density of fibers-   P_(m)=Density of matrix resin

The CPT is the theoretical thickness of an individual ply, which is afunction of the fiber areal weight, resin content, fiber density andresin density.

As an additional benefit, the veil, which is located at the interlaminarregion between plies of structural fibers and highly loaded with resin,may act as a carrier for materials such as toughening particles ortoughening fibers for further toughening of the resulting composite.

High quality slit tapes and slit tows may be obtained by sufficientlyhigh cohesion between the filaments. Good cohesion may prevent theindividual filaments from separating from the slit tape/tow during theslitting process and other subsequent handlings such as when thetape/tow is processed through the automated machines.

In some aspects, the liquid binder composition disclosed hereinpenetrates the structure of the unidirectional tape, prior to slitting,and keeps the filaments together. This penetration is also helpful tocontrol the width of the resulting slit tape.

In some embodiments, the type and amount of binder and/or sizing agentsdoes not impede the automated laydown process or the compositemanufacture in particular the resin injection, and does not alter themechanical performance of the composite or its T_(g).

In some embodiments, good lay down performance and high throughput isachieved due to attributes of the slit tape/tow, such as a good cohesionand stability, a good robustness to the process in particular agitationand friction, and the ability to tack to the tool or first ply, andsubsequent plies.

Tacking a ply of fibrous material to the tool or a previous ply may beachieved by using a binder that is heat activated during the laydownprocess. It is preferred that the binder does not impede the laydownprocess, the composite manufacture, the composite mechanicalperformance, or its T_(g).

Resin diffusion through a preform during the resin injection cycle maybe a function of the permeability of the preform and the direction oftravel of the resin compared to the distribution of the permeability.For example, in some instances infusing parallel to the plies of theunidirectional structural carbon fiber textile may be achieved easilywhile diffusing the resin through the thickness may be more challenging,due to gaps or very small gaps between the fibers of, for exampleunidirectional tapes, hence limiting the resin flow through thethickness. Providing perforations of the webs, such as about 10 per cm²,allows resin to flow sufficiently in the Z direction. The fabricationmode of the unilateral tape layer may affect the desirability of havingperforations to facilitate resin flow. For example, a through-thicknessair permeability of greater than 25 cc/min may be required for thepreform, and greater than 50 cc/min may be preferred, depending on theprocess window of the resin system used and thickness of preform to beinfused.

Binder Compositions

Binders have the various purposes such as for cohesion of the structuralfibers, for binding structural fibers, and to provide tack so thematerial remains in a stationary position during the lay down process. Abinder may be selected to help maintain cohesion of the fibers that formthe unidirectional or textile material layer during the slittingprocess. It is helpful if the binder does not impede the lay downprocess or the composite manufacture and in particular, the resininjection process. Binders for binding fibers may be reactive ornonreactive with the resin matrix when forming a composite material, andexamples include thermoplastic binders. The binder generally should notsignificantly affect the mechanical performance of the resultingcomposite nor lower its T_(g). In addition, it is preferred that thebinder is easy to process and have a low-cost.

A binder composition for treating structural fibers/textile material forthe purposes disclosed herein is a water-borne binder compositioncontaining one or more polymers selected from the group consisting ofpolyurethanes, aromatic polyhydroxyethers, copolymers, mixtures,reaction products or blends thereof, in combination with least oneaminoplast cross-linker, and optionally, a catalyst of sufficient acidstrength to catalyze the crosslinking reaction. The acid catalysts mayinclude, but are not limited to, proton donating acids such ascarboxylic, phosphoric, alkyl acid phosphates, sulfonic, di-sulfonicacids and/or Lewis acids such as aluminum chloride, bromide or halide,ferric halide, boron tri-halides, and many others in both categories asis well known to one skilled in the art. In a preferred embodiment, thecross-linker is a melamine-based cross-linker, for example, tri- tohexa-methoxyalkyl melamine class of aminoplast cross-linkers.

The polyurethane can be synthetized reacting a polyisocyanate with oneor more polyols having a number average molar mass (M_(n)) of at least400 g/mol, selected from a group consisting of aliphatic or aromaticpolyether polyols and polyester polyols and optionally:

-   -   a compound capable of forming anions and with at least two        groups that are reactive towards isocyanate groups;    -   a low molar mass polyol with M_(n) of from 60 to 400 g/mol;    -   a combination thereof.

Suitable polyisocyanates (which means compounds having a plurality ofisocyanate groups) for preparing the polyurethane include any organicpolyisocyanate, preferably monomeric diisocyanates. Especially preferredare polyisocyanates, especially diisocyanates, having aliphatically-and/or cycloaliphatically-bound isocyanate groups, althoughpolyisocyanates having aromatically-bound isocyanate groups are notexcluded and may also be used,

Examples of suitable polyisocyanates which may be used include ethylenediisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylenediisocyanate, 2,4,4-trimethyl-1,6-hexamethylene diisocyanate,1,12-dodecanediisocyanate, cyclobutane-1,3-diisocyanate,cyclohexane-1,3- and/or -1,4-diisocyanate,1-isocyanato-2-isocyanatomethyl cyclopentane,1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane(isophoronediisocyanate or IPDI), 2,4- and/or 2,6-hexahydrotoluylene diisocyanate,2,4′- and/or 4,4′-dicyclohexylmethane diisocyanate,a,a,a′,a-tetramethyl-1,3-and/or -1,4-xylylene diisocyanate, 1,3- and1,4-xylylene diisocyanate,1-isocyanato-1-methyl-4(3)-isocyanatomethylcyclohexane, 1,3- and1,4-phenylene diisocyanate, 2,4- and/or 2,6-toluylene diisocyanate,diphenyl methane-2,4′- and/or -4,4′-diisocyanate,naphthalene-1,5-diisocyanate, triphenylmethane-4,4′,4″-triisocyanate,polyphenyl polymethylene polyisocyanates of the type obtained bycondensing aniline with formaldehyde followed by phosgenation, andmixtures of the above-mentioned polyisocyanates.

Suitable polyols preferably have a number average molar mass (M_(n)) offrom 400 g/mol to 5000 g/mol. Examples of suitable polyols includealiphatic polyether polyols such as polyoxyethylene glycol,polyoxypropylene glycol, or mixed polymers of such units, polyesterpolyols obtainable by polycondensation of diols or polyols withdicarboxylic or polycarboxylic acids, such polyester polyols includingpolyethylene adipate, mixed polyesters derived from ethylene glycol,hexane diol, trimethylol propane, adipic and terephthalic acid, etc.Other building blocks that may constitute, or be included in, suchpolyester polyols are hydroxycarboxylic acids such as hydroxybutyric orhydroxy caproic acid or their lactones.

Suitable aromatic polyether polyols are epoxy resins or phenoxy resins,or mixtures thereof.

The terms “poly(hydroxyether)” and “phenoxy” herein refer tosubstantially linear polymers having the general formula:

*D-O-E-O*_(n)

wherein D is the radical residuum of a dihydric phenol, E is ahydroxyl-containing radical residuum of an epoxide and n represents thedegree of polymerization and is at least 30 and is preferably 80 ormore. The term “thermoplastic poly (hydroxyether)” is intended toinclude mixtures of at least two thermoplastic poly (hydroxyethers).

The dihydric phenol contributing the phenol radical residuum, D, may beeither a dihydric mononuclear or a dihydric polynuclear phenol such asthose having the general formula:

wherein Ar is an aromatic divalent hydrocarbon such as naphthylene and,preferably, phenylene, X and Y Which can be the same or different arealkyl radicals, preferably having from 1 to 4 carbon atoms, halogenatoms, i.e., fluorine, chlorine, bromine and iodine, or alkoxy radicals,preferably having from 1 to 4 carbon atoms, a and b are integers havinga value from 0 to a maximum value corresponding to the number ofhydrogen atoms on the aromatic radical (Ar) which can be replaced bysubstituents and R is a bond between adjacent carbon atoms as indihydroxydiphenyl or is a divalent radical including, for example,

and divalent hydrocarbon radicals such as alkylene, alkylidene,cycloaliphatic, e.g., cycloalkylidene, halogenated alkoxy or aryloxysubstituted alkylene, alkylidene and cycloaliphatic radicals as well asalkarylene and aromatic radicals including halogenated, alkyl, alkoxy oraryloxy substituted aromatic radicals and a ring fused to an Ar group;or R1 can be polyalkoxy, or polysiloxy, or two or more alkylideneradicals separated by an aromatic ring, a tertiary amino group, an etherlinkage, a carbonyl group or a sulfur-containing group such assulfoxide, and the like.

Examples of specific dihydric polynuclear phenols include, among others:

The bis(hydroxyphenyl) alkanes such as 2,2-bis-(4-hydroxyphenol)propane,2.4′-dihydroxydiphenylmethane, bis(2-hydroxyphenyl)methane,bis(4-hydroxyphenyl)methane,bis(4-hydroxy-2,6-dimethyl-3-methoxyphenyl)methane,1,1-bis(4-hydroxyphenyl ethane, 1,2-bis(4-hydroxyphenyl)-ethane,1,1-bis(4-hydroxy-2-chlorophenyl)ethane,1,1-bis-(3-methyl-4-hydroxyphenyl)ethane,1,3-bis(3-methyl-4-hydroxyphenyl)propane, 2,2-bis(3-phenyl-4-hydroxyphenyl)-propane,2,2-bis(3-isopropyl-4-hydroxyphenyl)propane,2,2-bis(2-isopropyl-4-hydroxyphenyl)propane,2,2-bis-(4-hydroxylnaphthyl)propane, 2,2-bis(4-hydroxyphenyl)-pentane,3,3-bis(4-hydroxyphenyl)pentane, 2,2-bis(4-hydroxyphenyl)heptane,bis(4-hydroxyphenyl)phenylmethane,bis(4-hydroxyphenyl)cyclohexylmethane,1,2-bis(4-hydroxy-phenyl-1,2-bis(phenyl)propane,2,2,-bis(4-hydroxyphenyl)-1-phenyl-propane and the like;

Di(hydroxyphenyl)sulfones such as bis(4-hydroxy-phenyl)sulfone,2,4′-dihydroxydiphenyl sulfone, 5′-chloro-2,4′-dihydroxydiphenylsulfone, 5′-chloro-4,4′-dihydroxydiphenyl sulfone and the like;

Di(hydroxyphenyl)ethers such as bis(4-hydroxy-phenyl)ether, the 4,3′-,4,2′-, 2,2′-,2,3′-, di-hydroxydiphenyl ethers,4,4′-dihydroxy-2,6-dimethyldiphenyl ether,bis(4hydroxy-3-isobutylphenyl)ether,bis(4-hydroxy-3-isopropylphenyl)ether,bis(4-hydroxy-3-chlorophenyl)-ether, bis(4-hydroxy-3flurophenyl)ether,bis(4-hydroxy-3-bromophenyl)ether, bis(4-hydroxynaphthyl)ether,bis(4-hydroxy-3-chloronaphthylether, bis(2-hydroxydiphenyl)-ether,4,4′-dihydroxy-2,6-dimethoxydiphenyl ether,4,4-dihydroxy-2,5-diethoxydiphenyl ether, and the like.

Also suitable are the bisphenol reaction products of 4-vinylcyclohexeneand phenols, e.g., 1,3-bis(p-hydroxyphenyl)-1-ethylcyclohexane and thebis-phenol reaction products of dipentene or its isomers and phenolssuch as 1,2-bis(p-hydroxyphenyl)-1-methyl-4-isopropylcyclohexane as wellas bisphenols such as1,3,3′trimethyl-1-(4-hydroxyphenyl)-6-hydroxyindane, and2,4-bis(4-hydroxyphenyl)-4-methylpentane, and the like.

wherein X and Y are as previously defined, a and b have values from 0 to4, inclusive, and R is a divalent, saturated aliphatic hydrocarbonradical, particularly alkylene and alkylidene radicals, having from 1 to3 carbon atoms, and cycloalkylene radicals having up to and including 10carbon atoms.

Mixtures of dihydric phenols may also be used, and whenever the term“dihydric phenol” or “dihydric polynuclear phenol” is used herein,mixtures of these compounds are intended to be included.

The epoxide contributing the hydroxyl containing radical residuum, E,can be monoepoxide or diepoxide. A monoepoxide contains one such oxiranegroup and provides a radical residuum E containing a single hydroxylgroup, a diepoxide contains two such oxirane groups and provides aradical residuum E containing two hydroxyl groups. Saturated epoxides,by which term is meant diepoxides free of ethylenic unsaturation,i.e., >C—C< and acctylenic unsaturation, i.e., —C≡C—, are preferred.Particularly preferred are halogen substituted saturated monoepoxides,i.e., the epichlohydrins and saturated diepoxides which contain solelycarbon, hydrogen and oxygen, especially those wherein the vicinal oradjacent carbon atoms form a part of an aliphatic hydrocarbon chain.Oxygen in such diepoxides can be, in addition to oxirane oxygen, etheroxygen -0-, oxacarbonyl oxygen carbonyl oxygen and the like.

Specific examples of monoepoxides include epichlorohydrins such asepichlorohydrin, epibromohydrin, 1,2-epoxy-1-methyl-3 -chloropropane,1,2-epoxy-1-butyl-3-chloropropane, 1,2-epoxy-2-methyl-3-fluoropropane,and the like.

Illustrative diepoxides include diethylene glycolbis(3,4-epoxycyclohexane-carboxylate),bis(3,4-epoxycyclohexyl-methyl)adipate,bis(3,4-epoxycyclohexyl-methyl)phthalate,6-methyl-3,4-epoxycyclohexylmethyl-6-methyl-3,4-epoxycyclohexanecarboxylate,2-chloro-3,4-epoxycyclohexylmethyl-2-chloro-3,4-epoxycyclohexane-carboxylate,diglycidyl ether, bis(2,3-epoxycyclopentyl)-ether, 1,5-pentanediolbis(4-methyl-3,4-epoxycyclohexyl-methyl)ether,bis(2,3-epoxy-2-ethylhexyl)adipate, diglycidyl maleate, diglycidylphthalate, 3-oxa-tetracyclo[4.4.0.17,10.02,4]-undec-8-yl2,3-epoxy-propyl ether, bis(2,3-epoxycyclopentyl)sulfone,bis(3,4-epoxyhexoxypropyl)sulfone, 2,2′-sulfonyldiethyl,bis(2,3-epoxycyclopentanecarboxylate), 3-oxatetracyclo-[4.4.0.17,10.02,4]-undec-8-yl 2,3-epoxybutyrate,4-pentenal-di-(6-methyl-3,4-epoxycyclohexylmethyl) acetal, ethyleneglycol bis(9,10-epoxystearate), diglycidyl carbonate,bis(2,3-epoxybutylphenyl)-2-ethylhexyl phosphate, diepoxydioxane,butadiene dioxide, and 2,3-dimethyl butadiene dioxide.

Examples of compounds capable of fanning anions include polyols,particularly diols, and polyamines, particularly diamines, orhydroxyamines, that carry from 1 to 3 carboxyl or sulfonic acid groupsper molecule.

Examples of carboxylate containing compounds of this composition includethe reaction of isocyanated terminated polyol pre-polymers (obtained bythe reaction of excess di-isocyantate with hydroxyl containingper-polymers) with hydroxyl containing carboxylic acids. Examples ofcationic terminated compounds of this invention include the quarternaryammonium or phosphonium prepolymers. Such cationic compositions can beprepared by the reaction of tert-amine containing alcohols with abovesaid isocyanated terminated pre-polymers followed by reaction with aquarterizing agent such as dimethyl sulfate or an alkyl halide as isknown by one skilled in the art.

Examples of low molar mass polyols with a molar mass of preferably from60 to 400 include ethylene glycol, diethylene glycol, 1,4-butane diol,cyclo-hexane diol and any other diol known to those skilled in the art.

Examples of preferred water borne phenoxy resin are condensationpolymers derived from bisphenol-A (2,2-bis(p-hydroxyphenyl)propane andepichlorohydrin having the structural formula:

Examples of polyhydroxyether water dispersions are Phenoxy PKHB, PKHHand PKIIC commercialized with the trade designation of PKHW 34, 35 and38 by InChem.

Suitable crosslinkers include aminoplasts, or amino resin cross-linkerswhich are the reaction products of either urea or melamine withformaldehyde and an alcohol. Besides urea and melamine, other compoundswith similar functionality such as benzoguanamines, glycolurils, cyclicureas, hydantoins, primary and secondary amides, carbamates etc., mayalso be used where certain property advantages are required.

The cross-linking reaction (“cure”) is principally one oftrans-etherification between hydroxyl groups on the primary polymericportion and alkoxymethyl or alkoxybutyl groups on the amino resin. Inaddition to the trans-etherification reaction, the amino resin almostalways undergoes self-condensation reactions to some extent, more orless dependent upon the amino resin type.

Another attribute of aminoplast cross-linkers is that their hydrophilicor hydrophobic characteristics can be tailored so that it is possible byone skilled in the art to select whether the amino resin crosslinkerresides predominately in the organic phase or the aqueous phase of theaqueous dispersions. There may be certain advantages for the amino resincrosslinker to reside in one phase or the other, particularly if it isdesired to apply the composition by different methods such as dipping,roller coating or spraying where one or both phases may or may not bedesired to remain on the substrate before curing.

The major by-products of the cure reaction include methanol and/orbutanol and water. Cure temperatures are typically in the range of 180to 465° F. (82 to 232° C.) for times that vary from 15 to 30 min at thelower end of the temperature range to perhaps only a few seconds at theupper end. There are highly catalysed amino resin formulations that cureat room temperature such as those found in the wood and plasticscoatings industry, but the majority of commercially availableformulations are typically cured at elevated temperatures and isdescribed in this invention.

In a preferred embodiment of this invention a monomericalkyloxymethylmelamine (Chemical Structure 1) with lower levels ofdimeric and trimeric analogs (respectively Chemical Structures 2 and 3)which are linked either through methylene, —N—CH₂N— or methyleneoxy—NCH₂OCH₂N— bridges may be used.

Structure 1. Monomer of Alkylated Melamine Aminoplast

where R is an alkyloxymethyl and preferably a methoxymethyl reactivegroup.

Structure 2. Dimer of Alkylated Melamine Aminoplast

where R is an alkyloxymethyl and preferably a methoxymethyl reactivegroup.

Structure 3.Trimer of an Alkylated Melamine Aminoplast

where R is an alkyloxymethyl and preferably a methoxymethyl reactivegroup.

Several catalysts may be optionally used to accelerate the cross-linkingreaction of the composition, depending on the cure temperature and theparticular amino resin used. Suitable catalysts include strong acidswhich are capable of catalysing the reaction between the aminoplast andthe resin, including super-acids and blocked versions thereof. In apreferred embodiment a blocked acid can be used to achieve high reactionrates while providing improved formulation stability and maintaining thepH value unaltered. Blocked sulfonic acid catalysts, for example,amine-blocked sulfonic acid catalyst, are particularly suitable.

In a preferred embodiment, the liquid binder composition is an aqueousdispersion containing a polyhydroxyether-polyurethane copolymer;methoxyalkyl melamine (for example, tri- to hexa-methoxyalkyl melamine)as an aminoplast cross-linker; and a blocked acid catalyst (such asblocked sulfonic acid catalyst), wherein:

-   -   a. the copolymer may have a number molecular weight (M_(n)) in        the 10000-100000 Da range and a polydispersity (M_(w)/M_(n)) in        the range between 1.1 and 5, and    -   b. the copolymer may have an average particle size (d50) in the        range between 0.1 and 50 microns.

The amount of binder applied to the fibers may be less than about 15% byweight, and preferably less than 10%, and more preferably less than 5%,such as 4%, 3%, 2% or 1%.

In some embodiments, the polyhydroxether portion of the copolymercontains a Bisphenol-A, and the polyurethane portion of the copolymer isbased on polyisocyanate and a polyol selected from a group consisting ofaliphatic or aromatic polyether polyols, and polyester polyols.

The disclosed binder composition may be used for the impregnation, atroom temperature, of self-supporting dry fibrous products suitable forautomated lay down processes (e.g., ATL/AFP) with no limitation to theproduct width. The binder may be applied to the fibrous products byliquid dip-coating, roller coating or spraying on the fiber web.Furthermore, the binder composition may be applied to the totality or tospecific areas of the fibrous product using standard manufacturingprocesses.

When the dry self-supporting unidirectional or textile material is usedin a resin injecting process, it is useful if the binder does not form acontinuous film at the surface of the unidirectional or textilematerial, which may prevent the resin from satisfactorily penetratingthrough the thickness of the preform comprising the unidirectional ortextile material during the resin injection cycle.

Fibrous Materials

The initial fibrous materials to be treated with the liquid binderdisclosed herein may be in the form of a self-supporting unidirectionaltape, for example, having a width ranging from about several inches wideto narrow widths as low as ¼ inch, or a non-crimp fabric. Theself-supporting unidirectional tape may be wound onto spools and can beused in the ATL/AFP process. The non-crimp fabric (NCF) containingunidirectional tows that are stitched together. The tows may or may nottouch each other such that gaps are present between tows thus providingpermeations in the material. In contrast, unidirectional tape does notcontain stitching because it contains a type of binder chemical thatkeeps the fibers together. Unifiber is a trade name for a product thatcontains fine threads that bind the fibers together such that there areno gaps or permeations.

In certain embodiments, a nonwoven veil composed of randomly arrangedfibers is laminated to a fiber web of structural fibers to form a drytape, which is subsequently coated with the liquid binder compositiondisclosed herein. The veil may provide permeability to the binder-coatedfibrous material. In some aspects, veils are made of structural materialsimilar to that used as structural fibers such as carbon, glass, andaramid. Other purposes of veils include a means for holding fiberstogether; however, this is not the primary importance of veils in thisapplication. The veil itself may contain additional binding ortoughening agents/particles.

The term “fibrous material” as used herein may include structural fibersor fibrous materials adapted for the structural reinforcement ofcomposites. The structural fibers may be made from high-strengthmaterials such as carbon, glass, and aramid. The fibers may take theform of any one of short fibers, continuous fibers, sheets of fibers,fabrics, and combinations thereof. The fibers may further adopt any ofunidirectional, multi-directional (e.g. two-or three-directional),non-woven, woven, knitted, stitched, wound, and braided configurations,as well as swirl mat, felt mat, and chopped mat structures. Woven fiberstructures may comprise a plurality of woven tows having less than about1000 filaments, less than about 3000 filaments, less than about 6000filaments, less than about 12000 filaments, less than about 24000filaments, less than about 48000 filaments, less than about 56000filaments, less than about 125000 filaments, and greater than about125000 filaments. In further embodiments, the tows may be held inposition by cross-tow stitches, weft-insertion knitting stitches, or asmall amount of resin, such as a sizing agent.

The fibrous product that has been treated with the binder compositionaccording to the present disclosure is a dry, self-supporting fibrousmaterial. The term “dry” as used herein refers to a material that may beconsidered to have a dry feel, which is not tacky to the touch andsubstantially without any matrix resin. The term “self-supporting”refers to a cohesive form of fibers or filaments that do not separatefrom each other, for example, during the slitting process and othersubsequent handlings such as when the fibrous product is processedthrough automated machines. For example, self-supporting refers theability of the dry, self-supporting fibrous product to maintain theintegrity of the fibrous material such as a favorable edge quality, thatis, a clean edge, with no bridging fibers, fuzz, or other observeddefects which otherwise could occur during the slitting process ifbinder treatment were not used. In some aspect, self-supporting fibrousproduct has edges after slitting that are substantially free ofprotruding dry filaments.

The binder-treated fibrous material can generally hold their positionwithout the need for an additional carrier fabric or scrim to keep thefibers from separating. Furthermore, the dry, self-supporting fibrousmaterial may be stored at room temperature, and does not need to berefrigerated due to the fact that it does not contain substantial amountof a matrix resin, in contrast to prepreg materials.

Veil

In some embodiments, a nonwoven veil may be used in addition to thebinder composition to improve the in plane permeability of the materialand favor the in plane resin flow. In some aspects, the veil may be avery light weight veil of about from 1 g to 8 g per square meter of thedry, self-supporting fibrous material, which is laminated thereto.

In addition, the veil may provide cross web direction stability to theunidirectional or textile material such as a unidirectional tape.

In a further beneficial aspect, the veil may be used as a carrier forcomposite toughening particles or fibers in the interlaminar region.

The veil may be of the same material nature than the fibers of theunidirectional or textile material or alternatively can be made of oneor more organic material such as some toughening thermoplasticmaterials. In addition, the veil may comprise a hybrid mix of both thesame type of fibers and at least one organic material.

The veil and the binder composition are used to aid the machine laydownof the fibrous material by application of heat (hot air, laser, or IR)and pressure via compaction roller. When polymer veils are used, thepreferred softening point of the polymer veils and binders is 150° C. orless in order to allow material to bond and form a consolidated preformat acceptable machine speeds.

In some aspects, the in-plane resin injection cycle is 3 times fasterthan a similar composite without a light-weight veil, consequently theachievable ply flow length is significantly improved by a factor of 7.

Perforations

In some embodiments, the binder-treated fibrous material containsperforations therein. “Perforation” as used herein may includeperforations through the entire thickness of the fibrous material.Perforated materials may provide air permeability above 50 cc/min, andallows infusion of preforms with thicknesses in excess of 30 mm inreasonable infusion times e.g.<4 hours.

Perforations may be performed either by needle punching, laser beamingor any other available methods to puncture the material through itsthickness. Perforation hole dimensions, usually the diameter, iscombined with the perforation density to achieve the expected airpermeability. More air permeability is needed for forming thickerpreforms i.e., with more plies, than with thinner preforms.

Usually a minimum of 20 cc/min is desirable for an effective flow of theresin. However, for preforms with thickness of more than 25 mm (1″) aminimum of 50 cc/min is desirable. Of course the desired airpermeability may be also a function of the resin viscosity and theprocessing conditions in particular temperature and part complexity.

For perforated materials, the fibers forming the unidirectional (UD)fiber web preferably do not move and cover the perforated holes, afterthe perforation step has been performed, otherwise the gain in airpermeability would be reduced or nil. The binder composition disclosedherein previously keeps the fibers together and prevent them fromcovering the perforated holes.

Perforation of the fibrous material also includes creating some smallslits or gaps between the fibers during the process of forming the UDfiber web.

Preform

The term “preform” or “fiber preform” as used herein include an assemblyof fibers, layers of fibers, or fabric plies, such as unidirectionalfibers and woven fabrics that are ready for receiving a liquid resin ina resin infusion process.

It has been found that using the self-supporting, binder-treated fibrousmaterial, in some instances, results in high-performance composites madevia a resin infusion process.

EXAMPLES

The following examples relate to dry unidirectional (UD) fiber materialsfor ATL/AFP application.

Example 1

The following fabrics were used in this Example.

(1) A unidirectional non-crimp fabric (UD NCF), supplied by Saertex,shown in FIG. 1. This fabric is produced at 50 inches wide. Carbon towdefinition is very much present and intertow gaps are up to 2 mm wide.Polyester stitching thread keeps the carbon tows together. Finepolyester threads are laid down across the fabric to provide lateralintegrity and stability to the fabric.

(2) A spread out web with binder yarns (Sigmatex Unifiber fabric) shownin FIG. 2. Carbon tows are spread out and held together by epoxy coatedglass threads on both sides of the tapes. There are no intertow gaps ormarginal gaps.

Both fabrics were binder coated with a thermoplastic-modified,epoxy-based binder (Cycom® 7720 from Cytec Engineered Materials). Apowder scattering method was used to deposit about 5 gsm of the bindercomposition on both faces of each fabric. The fabrics with the scatteredpowder were run through a double belt press to further drive the binderthrough the fiber web and insure a good cohesion of the UD fiber web.This is called a stabilization step. In addition, a very light weightcarbon veil with a fabric areal weight of 4 gsm was laminated onto oneof the faces of each fabric at the same time the fabric was run throughthe double press to fix the binder. Double belt processing conditionswere a speed of 2 m/min and a temperature of 210° C. The laminated,stabilized fabrics were very stable yet malleable, allowing manipulationto the desired shape without fibre loss or edge fraying.

Then the stabilized fabrics were slit to 50 mm wide tapes having a widthvariation of less than +/−1.0 mm. Edge quality of the slit tapes wassufficiently clean with limited bridging fibers, fuzz and or otherobserved defects. However, the product quality could be further improvedfor the manufacturing of large aircraft components using high speedautomated production processes.

Example 2

A series of different catalyzed and uncatalyzed binding agents based onpolyhydroxyether or polyurethane families, copolymers or combinationsthereof were mixed according to the compositions disclosed in Table 1.EP1 is a 53% solid aliphatic epoxy novolac emulsion commercialized byCOIM (Italy). PU1 is a 52% solid water dispersion of a2,2-bis(4-hydroxyphenyl)propane modified polyurethane with an numberaverage molecular mass of ˜30000 Daltons. The polyurethane portion wasobtained by reaction of isophorone diisocyanate and polypropyleneglycol. PU2 is a 40% solid self-cross linkable thermoplasticpolyurethane dispersion in water commercialized by BASF while PU3 andPU4 are respectively 43% and 34% solid self-crosslinkable polyesterurethane dispersions in water commercialized by Bayer Material Science.PHE1 is 34% solid polyhydroxyether emulsion in water available fromInchem (US).

TABLE 1 Binder compositions Binder Resin water emulsion (g) Cross-linker(g) Catalyst (g) DIW^(††) code EP1 PU1 PU2 PU3 PU4 PHE1 AMM* MAPI^(†)b-p-TSA^(‡) (g) 1a 100 — — — — — — — — 100 1b 100 — — — — — 5 — 3.5 1001c — 100 — — — — — — — 100 1d — 100 — — — — 5 — 3.5 100 1e —  50 50 — —— 100 1f — — 100 — — — — — — 100 1g — — 100 — — — — 10 — 100 1h — — —100 — — — — — 100 1i — — — 100 — — — 10 — 100 1l — — — — 100 — — — — 100*AlkylatedMethylMelamine (AMM) ^(†)Modified Aliphatic PolyIsocyanate(MAPI) ^(‡)Blocked p-ToluenSulfonic Acid (b-p-TSA) ^(††)Deionized water

The binding agents were used to dip-coat the same unidirectionalnon-crimp fabric (Saertex, Germany) described in Example 1.

The binder-coated fabrics were evaluated for drape-ability, anti-frayingbehavior, shrinkage, and self-bond ability. Drape was determined byhot-draping at 145° C. (3° C./min temperature ramp rate from roomtemperature) for 1 minute a 350×350 mm coated fabric onto a conic tool(height=86 mm, internal diameter=120 mm, external diameter=310 mm) undervacuum (60 mmHg vacuum throughout the test) and determining the numberof creases. Materials giving less than 6 creases were consideredexcellent (A), materials resulting in 6-12 creases were consideredacceptable (B) while materials producing more than 12 creases wereconsidered unacceptable (C).

Anti-fraying behavior was determined in a developmental controlledtension fuzz tester having four sections (let-off, friction rollers,catch plate and winder) running at a speed of 20 m/min. The amount offuzz accumulated on the catch plate over a period of 5 minutes wasweighted and materials ranked accordingly. Fuzz is the debris given offby tows rubbing against the friction rollers and collected by the catchplate. Materials resulting in more than 500 mg of fuzz were consideredunacceptable (C), materials giving off between 200 mg and 500 mg whereconsidered acceptable (B) whereas materials creating less than 200 mg offuzz were considered excellent (A). Shrinkage was determined bymeasuring the width of the pristine and binder coated fabric after theheat treatment (3 minutes at 100° C.+4 minutes at 130° C.). Materialsresulting in less than 1% shrinkage were considered excellent (A),materials giving 1-2% were considered acceptable (B) while materialsgiving more than 2% were considered unacceptable (C). Self-bond abilitywas determined by applying a 10N pressure using a compaction roller at atemperature of 100° C. for 5 seconds. The results are shown in Table 2.

TABLE 2 Physical properties of binder coated fabrics Binder Anti- Self-Fabric content fraying bond code Binder (w/w %) Drape behavior Shrinkageability 2a 1a 3 A B A B 2b 1b 3 A B A C 2c 1c 1 A B A B 2d 1d 1 A A A A2e 1d 2 A A A A 2f 1e 4 C A B B 2g 1f 2 B B B B 2h 1f 3 A B A B 2i 1g1.5 A B A A/B 2l 1g 3 A A A A/B 2m 1h 5 A A A A 2n 1h 2.5 A A A A 2o 1i5.0% A B B B/C 2p 1i 2.5% A B B B/C 2q 1i   1% A B A C 2r 1l 3.0% B B BC A = excellent B = acceptable C = unacceptable

Depending on the binder composition and content on the fibrous product,a specific pattern of physical properties can be achieved using thebinder compositions described in Table 1.

Example 3

Some of the binder compositions disclosed in Table 1 were used to dipcoat at room temperature the same unidirectional non-crimp fabric(Saertex-Germany) described in Example 1. All the coated fabrics werethen dried for 3 minutes at 100° C. and then for 4 minutes at 130° C. inan oven.

The binder-coated non-crimp fabrics were then cut into smaller plies andthe plies were laid-down in a stacking sequence. The layup was thenpre-formed in an oven at 130° C. for 30 minutes and infused with Prism®EP2400 (toughened epoxy system available from Cytec EngineeredMaterials). Panels having a V_(ƒ)(fiber volume fraction) in the 55%-57%range were produced after curing the infused preforms at 180° C. for 2h.

For comparison purposes, the same pristine (uncoated) unidirectionalnon-crimp fabric was used to prepare otherwise identical test panels(Control 1). A variety of mechanical tests were carried out on thepanels and the results are shown below in Table 3.

TABLE 3 Thermo-mechanical performance of Prism ® EP2400 infused panels 0CS 0 TM ILSS 0 CM (GPa) (MPa) (GPa) TS (MPa) (MPa) Tg (° C.) PanelBinder EN2850 EN2850 EN6035 EN6035 EN60 EN6032 Control 1 — 134.1 1226.2147.1 2310.4 80.6 173.2 3a Ex. 2d 131.5 1143.2 136.3 2266.8 93.2 163.83b Ex 2i 137.3 833.0 134.8 2245.5 77.6 161.4 3c Ex. 2q 133.5 1054.8125.4 2176.2 41.6 172.3

Example 4

Intermediate modulus carbon fibers (Tenax IMS 65) were formed into a 12″wide unidirectional web of 196 gsm using a prepreg tape machine while a4 gsm carbon veil and 5 gsm of thermoplastic-modified epoxy-based binderwere laminated to the unidirectional web on the same prepreg tapemachine. The resulting unidirectional tape was subsequently liquidcoated with the binder described in Example 2d to achieve a 3 gsm bindercoating. SEM pictures, FIGS. 3 and 4, show on both the veil side andfiber web side the presence of the binders which do not form a film,each having distinctive morphology with binder described in Example 2dforming droplets smaller than the carbon fiber diameter while the otherbinder forms much larger binder particle sizes that overlap severalfibers but do not form a film.

This unidirectional tape was then slit into multiple tows of differentwidths. Each tow width was measured using an electronic automatedmeasurement device equipped with a very fine resolution digital camera.About 2900 measurements were collected for each tow width. Table 4 belowsummarizes the measurement analysis.

TABLE 4 Target and experimental slit tape widths Target width 4.3005.400 5.800 6.000 6.100 6.350 Measured data mm Avg 4.295262 5.4088425.814885 6.050919 6.12134 6.34403 Max 4.471 5.638 6.147 6.174 6.36 6.44Min 4.151 5.23 5.695 5.919 6.041 6.28 Std dev 0.031464 0.047753 0.0303490.040826 0.026212 0.024468 COV 0.007325 0.008829 0.005219 0.0067470.004282 0.003857

In Table 4, COV is the coefficient of variation and it is calculated bydividing the standard deviation (Std dev) by the average (Avg).

Example 5 Comparative Example—Z Direction Permeability Evaluation

The z direction resin permeability of the material described in Example4 (6.35 mm-¼″ wide) was compared to the one of a commercial bindercoated/formed carbon tow (IMS60 24K) of equal width and similar arealweight.

Preforms were manufactured using an AFP machine with a laser head tocompact dry fabrics by applying approximately 100N pressure and a localsurface temperature in the 120° C. -180° C. range. 150×150 mmquasi-isotropic preforms of approximately 10 mm were laid-down with atarget gap setting of 0 mm between adjacent tows.

Preforms were then infused with Prism® EP2400 (toughened epoxy systemavailable from Cytec Engineered Materials) at 100° C. using a baggingarrangement to promote through thickness resin flow and a vacuum of <5mbar. The volume of infused resin was monitored over time.

FIG. 5 shows the relative volume of resin infused through the preformthickness as a function of time.

The preform manufactured using the material described in Example 4resulted in the best permeability values allowing the entirety of theresin to flow through the preform thickness in less than 1 hour whileonly the 20% of the resin volume penetrated the formed tow preform inover 1 hour due to the inferior width tolerance of the product, itspropensity to nest during the lay-down process and the resulting highvariation in local CPT.

1-22. (canceled)
 23. A fibrous tape suitable for automated tape laying,comprising: a ply of structural fibers laminated to a nonwoven veilcomprising randomly-arranged carbon fibers; a first binder compositiondistributed onto the structural fibers and the nonwoven veil, saidbinder composition comprising (i) one or more polymers selected frompolyhydroxyethers, polyurethanes, a mixture thereof, a copolymerthereof, and a reaction product thereof, and (ii) a methoxyalkylmelamine aminoplast cross-linker, wherein the ply of structural fiberscomprises unidirectional carbon fibers, and the fibrous tape ispermeable to liquid resin.
 24. The fibrous tape of claim 23, wherein theply of structural fibers is not bonded to another layer other than thenonwoven veil.
 25. The fibrous tape of claim 24, further comprising asecond epoxy-based binder, which comprises one or more multifunctionalepoxy resins and a thermoplastic polymer.
 26. The fibrous tape of claim23, wherein said tape has a width of 24 inches or less.
 27. The fibroustape of claim 23, wherein said tape has a width of 1.5 inches or less.28. A method comprising laying up a plurality of the fibrous tape ofclaim 23 in an automated process to form a preform that can be infusedwith a liquid resin.